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Exogenous vasopressin modulates activity of oxytocin neurons in homozygous Brattleboro rats

American Journal of Physiology 251(5 Pt 1): E556-E562
Exogenous vasopressin modulates activity of oxytocin neurons in homozygous Brattleboro rats
We studied the effects of chronic replacement with arginine vasopressin (AVP) or 1-desamino-D-arginine vasopressin (DDAVP), as well as acute replacement with AVP or DDAVP, on the responsiveness of oxytocin (OT) neurons as indexed by plasma oxytocin-associated neurophysin concentration ([OT-RNP]) during acute salt loading in conscious, chronically catheterized homozygous Brattleboro (DI) rats. Salt loading was carried out on days 5 and 12 of AVP (3,000 ng/day) or DDAVP (50 ng/day) treatment or 60 min after intraperitoneal injection of 1 .mu.g AVP or 24 ng DDAVP. All vasopressin treatments did not significantly alter the basal [OT-RNP]. In response to infusion of 18% saline, there were corresponding significant increases in plasma osmolality (Posmol) and [OT-RNP] in all animals. The increases in [OT-RNP] in vasopressin-treated DI rats were markedly reduced compared with those observed earlier for untreated DI animals despite similar rises in Posmol. The slopes of the relationship between .DELTA.[OT-RNP] and .DELTA.Posmol were 9.0 and 9.8 fmol .cntdot. ml-1 .cntdot. mosmol-1 .cntdot. kg for chronically AVP-treated DI rats, 8.9, and 8.8 fmol .cntdot. ml-1 .cntdot. mosmol-1 .cntdot. kg for chronically DDAVP-treated DI animals, 10.7 fmol .cntdot. ml-1 .cntdot. mosmol-1 .cntdot. kg for acutely AVP-treated DI rats, and 8.3 fmol .cntdot. ml-1 .cntdot. mosmol-1 .cntdot. kg for acutely DDAVP-treated animals compared with that of 34.9 fmol .cntdot. ml-1 .cntdot. mosmol-1 .cntdot. kg for untreated DI rats. The reduced responsiveness of OT neurons to acute salt loading in AVP- and DDAVP-treated DI rats implies a role of vasopressin in the regulation of OT release. Although this modulatory effect of vasopressin may be mediated via multiple mechanisms, it is believed to be chiefly mediated via a V2-like receptor rather than a V1-like receptor because it is produced by both exogenous AVP and DDAVP in amounts relative to their antidiuretic potencies. However, it is possible that receptors other than V2-type, such as V3-receptors, are involved in the effects of vasopressin on OT release in DI rats.

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Accession: 005419144

PMID: 3777164

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